A
pendulum is a clever timing device that was once used to help clocks
keep time. If you were making a clock, you would need to know all
about pendulums.

Does the time
for a swing depend upon the size of the swing? How does the pendulum
change its speed while it is swinging?

You can begin
to answer these questions using a sensor connected to a PC.

One complete swing of a pendulum - back and forth - is called a
period. The size of a swing is called the amplitude.

Setting up

Set up your apparatus as shown above.

1.

Connect
a position or angle sensor to the interface. Connect the interface
to the computer.

2.

Get
the computer ready to measure the position of the pendulum arm over
10 to 30 seconds.

3.

Start
the computer recording and the pendulum swinging.

4.

Adjust
the sensor to reset the computer to read zero when the pendulum
is at rest.

5.

Start recording on the computer only when you start to move
the pendulum.

6.

Try
to get the computer to let you keep two or more sets of swings
on the screen.

Make a
plan
Your task is to find out if the size of the swing affects the
time for a swing. You will need to record several swings - some
large and some small. Decide whether you will start with a large
swing and then try smaller ones - or whether you will start with
a small swing and then larger ones.

Questions

1.

Study
the graph. How can you tell that the pendulum is at the mid-point
of its swing?

2.

With
your graph on the screen, use the computer to read off the
time for large and small swings.

3.

Is there
a simple pattern in the results? Why then are pendulums used
in clocks?

4.

Choose
one of the peaks on the graph. Use the computer to read off
the gradient at the different points shown in the diagram.
Print the graph and label the points where:the
pendulum speed is highestthe
pendulum speed is lowestthe
pendulum speed is increasingthe
pendulum speed is decreasing

Extensions
How does the mass of the ball affect the period of a swing?
Do an experiment where you measure the periods of large, medium
and small balls.